Girdling Peach Trees in the Southeast

Arlie A. Powell, Horticulturist - Fruits,
Auburn University, AL

May 1996

GIRDLING PEACHES FOR PROFIT - A REVIEW OF THE PRACTICE

Girdling (removal of a strip of bark tissue) is a practice that has
been used on fruit plants for centuries. California as well as the countries
of Israel and South Africa utilize girdling as a regular part of their
cultural program on peaches and nectarines. Following years of experience,
growers in California have ably mastered the art of girdling to accomplish
two primary goals, namely to increase fruit size and earliness of harvest.
They presently girdle practically all early peach varieties through the
Coronet season. Their early nectarine varieties are handled in a similar
fashion. California's Marketing Order usually imposes a minimum 2 1/4 inch
(88 count) size (for shipping) on their earliest peach varieties. Girdling
is one of the main tools that enables California growers to ship such a
large minimum size so early in the season.

Before 1979 no girdling was being done in the Southeast. As a result
of some preliminary studies we conducted in 1978 and 1979 in south Georgia
and north Florida, girdling became a recommended practice (on trial basis)
in commercial plantings in Alabama, Florida, Georgia and South Carolina.

To further determine how well girdling would work under southeastern
conditions, studies were conducted in commercial plantings in Alabama from
1979 through 1984. The results of these studies were very promising and
indicated that girdling of early peach varieties could prove safe and quite
profitable for growers when the practice is properly used. After
several years of girdling trees in commercial plantings (especially in
Georgia and Alabama) during the early 80's, this practice has become well
accepted and utilized across the southeastern peach belt.

Although an increase in fruit size (by 1/8 to 1/4 inch in diameter)
and greater earliness of harvest are two of the most important benefits
of girdling, several other valuable benefits may be gained from this practice.
Among the most noteworthy are: (1) an increase in yield by 1/4 to 1/2 bushel
per tree, (2) fewer pickings (usually 2 to 4 compared to the normal 3 to
5) and a greater percentage of crop is harvested during the first picking
(an enhanced concentration of ripening), (3) an increase in red skin color
(helps in meeting USDA color standards), (4) use of an outstanding variety
to partially or completely replace (by moving harvest season forward) an
earlier poorer performing variety, (5) where desirable, the harvesting
period for a large block of a single variety may be split, and (6) provides
a fruit sizing benefit generally equal or superior to that realized from
extensive and costly bloom thinning of early varieties. This permits the
grower to adequately size early peaches without risking an increased crop
loss from freeze damage following bloom thinning. But with all practices,
the bottom line is profit, and our demonstration studies in Alabama have
shown that girdling can increase gross income per acre by several hundred
dollars (about $250 to $800 per acre).

Girdling has primary value for early varieties which characteristically
have smaller fruit size and lower yields than mid and late-season varieties.
Varieties vary somewhat in their response to girdling (some give more fruit
size and yield increase than others, etc.). However, all of the early varieties
we have studied thus far have responded quite well to the treatment.

Earliness of harvest is very important to growers because prices usually
start high at the beginning of the season and steadily fall until they
"bottom out" in early to mid July. Some recovery in price usually occurs
after this date. Through the use of girdling we have been able to consistently
advance the first harvest date of very early varieties such as Camden and
Springold by at least 3 to 4 days, Rubired by 7 days, while harvest of
the later maturing Redhaven is advanced by nearly 10 days. It should be
obvious that the harvest dates of later maturing varieties are advanced
much more than for early varieties. In general, the following chart applies
to how much the harvest date can be advanced by girdling:

Days Variety Ripens Before Elberta

Number of Days1 Ripening is Advanced

50 to 60

3 to 5

35 to 45

6 to 8

30 and earlier

9 to 12

1 Note:
if soil moisture is inadequate the advance in harvest date will be sharply
limited.

Recommendations on Using Girdling

Definition of terms is very important in understanding the difference
between girdling and scoring. Both of these practices have been evaluated
in our demonstration work. Girdling refers to the cutting and removal of
a strip of bark tissue from the trunk or scaffold branch (Figure 1). This
is achieved with a specially designed girding knife (Figure 2). Scoring
involves the severing of bark tissue (to the wood) with a knife, but no
bark tissue is removed (Figure 3). A large-bladed knife of any type is
satisfactory for scoring but a tile knife is ideal (Figure 4). For optimum
results with the least detrimental effect, girdling (or scoring) must be
done correctly. The following are suggestions for growers who wish to use
the practice in their orchards:

Type of Trees and Varieties to Girdle

Generally only early season varieties need girdling (those ripening
30 or more days ahead of Elberta). This includes varieties ripening as
early as Goldcrest and Camden and as late as the Maygold-Sentinel season.
Girdling will work quite well on later maturing varieties but generally
is not needed for adequate sizing. An exception would be a variety like
Redhaven which has a sizing problem. Also, if there is a need to ripen
part of a block of trees earlier, girdling could be used.

Girdle trees in their 5th leaf or older. Trees in 4th leaf may be girdled
if they have attained good size and base of scaffold branches are at least
2 inches in diameter. Please note that trees in their 3rd and 4th leaf
may be scored (preferably branches only) to enhance fruit size and earliness.
Scoring is as good as girdling on some varieties but not as good on others.
One of the main limiting factors in using scoring is the problem of growers
being able to inspect trees to make certain cuts are being properly made
(very difficult to see cuts and also know if they are deep enough).

Use only vigorous, healthy trees for girdling. Avoid girdling trees
which appear weak and are under stress of any kind. This includes trees
with gummosis or insect damage.

Only girdle trees which have full fruit crops. Girdling trees which
have reduced crops because of poor set or damage by freezes and hail is
not advisable. This could result in excessive sizing in some varieties
and increased fractured or split pit problems.

Description of the Girdling/Scoring Process

There are at least three sizes of girdling knives available based on
the width of cut, 1/8 inch, 3/16 inch and 1/4 inch. The 1/8 inch knife
is recommended for younger, thinner barked trees (4th to 8th leaf) because
complete healing of the cut area is realized quicker and with less difficulty.
However, if properly used the 3/16 inch knife also works well. The use
of a 3/16 inch knife should be restricted to 9th leaf trees and older having
large scaffold limbs with thicker bark. It is easier to cut thicker bark
with a wider blade. The wider the cut, the longer the time required for
healing. In the case of very vigorous varieties such as Bicentennial and
Springcrest, a wider cut might prove of value in allowing for more time
for sizing of fruit. It is suggested, however, that growers learn the "art"
of girdling first using the 1/8 inch knife. The 1/4 inch knife as used
in California is not recommended.

Girdle the lower portions of the primary scaffold branches (Figure 5).
Do not girdle trunks. Only girdle branches 2 inches in diameter and larger.
The greater the diameter of the branch generally the more rapid and complete
is the recovery process. Girdling of small branches can result in limited
recovery and death. Girdling of trunks is not recommended.

Use an "S" (spiral) girdle rather than a complete girdle. A complete
girdle is one in which the beginning and ending portions of the cut are
brought together at the same point. An "S" girdle involves starting the
cut at one point on the branch and ending the cut in line with the beginning
cut but 1 to 2 inches above or below it (Figure 1). Thus the two ends of
the cut forming the "S" girdle are separated by 1 to 2 inches of bark.
Both types of girdling give the same results in terms of fruit size increase,
etc., but the "S" girdle provides a higher degree of safety and recovery
of the tree.

If scoring is used, it should be done at the recommended time for girdling.
Two parallel cuts should be made about 1 inch apart on each scaffold branch
with a tile knife (or equivalent) that has about 1/16 inch blade. Each
of the two cuts should connect making a complete circle (Figures 3 &
4). It seems that the effectiveness of scoring may vary among varieties
more so than girdling (scoring effect may not be as pronounced as girdling).
For example, scoring has worked equally as well as girdling in sizing JuneGold
fruits, but not quite as good as girdling with the Camden variety.

Proper Timing of Girdling

Girdling should be done approximately 4 to 8 weeks before normal harvest
time. The final 10 to 20 days just ahead of complete pit hardening is
ideal. For very early varieties such as Springold and Camden, this
means girdling should be done about 4 weeks after bloom, which is about
4 weeks ahead of normal harvest. Where necessary these varieties may be
girdled 2 1/2 to 3 weeks after bloom.

It is important that fruit thinning and girdling not be done at the
same time because of the excessive shock to the tree and remaining fruit.
This could cause an undesirable increase in the number of fruits with split
pits. Ideally, trees should be thinned and then girdled several days later
(allow at least 4 to 5 days between thinning and girdling). However,
if it becomes necessary, trees may be girdled first and fruit thinning
completed several days later. If a little follow up thinning is needed
(after bulk of thinning is completed) this may be done within 2 days after
girdling with no problem.

Special Precautions/Suggestions

Girdling trees twice during the same season is not advised. Some
growers have tried this approach because of serious problems in sizing
fruits of certain varieties. Reportedly, some growers in California utilize
this practice on one or more extremely vigorous varieties.

If a particular orchard is being girdled it is generally not necessary
to bloom thin in order to produce adequate fruit size. However, with a
real problem variety both practices could be combined to maximize fruit
size. If this approach is followed the grower may observe some increase
(though usually tolerable) in the level of visible split pits as compared
to a tree that was bloom thinned only.

Callousing and complete healing of wounds normally takes only 3 to 4
weeks but may require another week or two in some cases (Figure 7). During
the healing period, the girdling wounds are sometimes infested by lesser
peach tree borer. Thus, during the period from girdling until harvest (4
to 7 weeks) attention should be given to directing the normal cover sprays
to provide reasonable control of borers during this period. Once harvest
is completed, a borer spray should be applied to lower portions of branches
and trunk for season long control. This spray will normally be applied
during June.

Trees under drought stress will fail to size their fruit adequately
even if girdled. Irrigation (or rainfall) is essential in realizing the
maximum effect from girdling. Where only periodic irrigation is being used,
try to complete final irrigation no closer than 8 to 10 days before harvest.

Girdling does not replace the need for proper fruit thinning.
Both practices are essential for developing optimum fruit size of early
varieties.

Girdling places trees under considerable stress while they are maturing
their crop. Therefore, it is recommended that mature, bearing trees receive
at least 60 to 75 pounds of nitrogen per acre (such as 600 to 750 pounds
of 10-0-10) during late January- February. Following harvest, girdled trees
should receive an additional 20 to 40 pounds of nitrogen per acre such
as 200 lbs./acre of calcium nitrate or 100 lbs./acre of ammonium nitrate
(or other equivalent nitrogen source). A postharvest application of nitrogen
is a part of the ten-point program for managing peach tree short life.
The above fertilizer rates are provided as general guidelines and may be
adjusted upward or downward based on previous fertilization experience,
tree size, crop load and type soil involved. Maintaining good vigor is
especially important for varieties susceptible to bacterial spot.

In result demonstration studies conducted since 1979, no problems with
girdling the same trees in successive years were observed so long as good
tree vigor was maintained and lesser borers were controlled. Thus, where
proper nutrition and pest management are maintained, annual girdling of
the same blocks works well.

Because of potential disease problems in all peach orchards, girdling
knives should be dipped in a chlorine solution (9 parts water plus 1 part
liquid chlorox) between blocks or rows of trees as conditions dictate.
Although diseased trees should not be girdled, there is always the possibility
a given block may have some diseased trees that are cut. If an area is
free of gummosis, be certain all tools are treated before use in that block
to avoid introducing the problem. After chlorine treatment, spray with
an oil (such as WD-40 or equivalent) and wipe clean, otherwise the blade
will corrode.

For growers who are interested in girdling but have never used the practice,
it is suggested that only small blocks of trees of early varieties be
used in initial testing. Only after having gained experience and confidence
in using girdling on a few trees should growers consider extensive use
of this practice.

Special Considerations at Harvest Time

Special attention should be paid to harvesting of blocks which have
been girdled. Ripening of fruits on girdled trees occurs appreciably faster
and must be more closely monitored by the grower. This greater speed of
ripening is not as obvious in extremely early varieties such as Camden.
However, it is definitely more noticeable with later ripening varieties
such as Rubired and Redhaven (Figure 6).

The key in maintaining good firmness in fruit on girdled trees is to
harvest at normal shipping maturity. Don't allow fruit to hang too
long. Fruits do not have to be harvested every day but the grower should
never allow more than one or two days between individual pickings. The
grower who has a roadside market and wants to sell only tree-ripened fruit
will have to harvest at least every other day.

Costs of Girdling Trees

Custom girdling costs usually vary from $.20 to $.75 per tree depending
on difficulty of job. Young trees with only 3 to 5 properly arranged scaffold
branches may only cost $.20 to $.30 per tree (Figure 8). Experienced workers
can girdle about 100 trees or nearly an acre per 8-hour day. However, in
some orchards workers may double this rate. Older, poorly trained trees
are more difficult and costly to girdle (may cost $.50 to $.75 per tree).

Sources For Girdling Knives

The best and most economical source of girdling knives is VACA Shears,
Fresno CA. This used to be part of Malaga Maid Manufacturing, the company
that supplied knives in the past. Other companies such as Farmer's Buying
Service, Fresno CA, Growers Supply, Reedley, CA and Michigan Orchard Supply
Co., South Haven, MI, sell girdling knives to growers which they apparently
purchase from VACA or other sources. For obvious reasons it is usually
more economical for growers to obtain knives from a basic manufacturer
than from a retailer, although they may be purchased from any of these
companies.

It is recommended that growers purchase girdling knives without a scraper.
These knives retail for around $24.00 each, but growers may be able to
order them directly from the company at about a 40% discount. To order,
growers should phone the company and ask about the shipping charge. Once
this is determined they may forward their check for the total amount and
the shipment should be received in a few days. The other method of ordering
is to call the company, place the order and pay for the shipment C.O.D.